The present invention discloses an optical sensor for detecting and/or quantifying oxygen based on a luminophore dispersed in a polymer matrix and methods for using said sensor, often for the purpose of monitoring chemical and biological processes.
Oxygen sensors for fluids fall into two general categories, electrochemical sensors and optical sensors.
Electrochemical sensors typically employ an electrode that is placed in a fluid in which oxygen is to be measured. The basic principal is that the electrode has both a cathode and an anode. Oxygen enters the electrode, typically through a permeable membrane, and is reduced at the cathode, creating a measurable electric current. Note that an electrochemical sensor measures an ionic current, the specificity to oxygen is determined solely by the ability of the permeable membrane to exclude unwanted species. The current produced is proportional to the oxygen concentration. While these sensors are considered the “gold” standard for measuring oxygen due to the long history of use, they suffer from significant limitations; including consuming oxygen (the analyte being monitored), requiring a flowing fluid, being sensitive to environmental factors, and drifting over time (due to electrolyte consumption).
Optical sensors typically use luminescent molecules embedded in a sensing film that is placed in the fluid in which oxygen is to be measured. The luminescent molecules are photoexcited and either the lifetime or intensity of the emitted luminescence is measured. Due to changes in the luminescence caused by the presence of oxygen, said measurement is indicative of oxygen concentration. Current optical oxygen sensors suffer from degradation, called “photobleaching,” which limits the total number of measurements possible with a single sensor, forcing the choice between frequent measurements over a short period or a sparse data set over a long period, as shown, for example, in Draaijer U.S. Pat. No. 7,695,679 for the Ru complexes and S. M Borisov, G. Nuss 7 I. Kimant, Anal. Chem 80 9435 (2008) for the Pt and Pd porphyrines. Current optical oxygen sensors cannot simultaneously satisfy the requirements of (i) sensitivity, (ii) specificity to oxygen, i.e. lack of cross sensitivity to other species in the fluid, (iii) continuous monitoring without restrictions on the data collection protocol, and (iv) minimal coupling to changes in the environment.
Real-time detection of oxygen in fluids is important for a variety of chemical and biological processes ranging from aquaculture to industrial process control. For example, dissolved oxygen is considered a principal limiting factor in aquaculture production systems. Bio-reactors and the food/beverage industry require real-time monitoring of oxygen for process control. Water quality and environmental applications such as EPA remediation sites, monitoring the impact of oil spills on marine biology, and mining require continuous (24/7) remote oxygen monitoring. Bio-medical applications such as in-vitro studies of the anaerobic growth of cancer cells and in-vivo measurements of dissolved oxygen in organs or tissue require oxygen sensors that are not affected by constituents of the fluid under study. However, current oxygen sensors do not possess the capabilities needed for such applications.
An oxygen sensor for such applications preferably possesses a number of key attributes. First, such a sensor is preferably unaffected by environmental factors such as salinity, pH, phosphates, CO2, and biological waste, all with a minimum temperature dependence. Second, such a sensor preferably provides for real-time continuous monitoring of oxygen without limitations on the number of data points. Third, such a sensor preferably exhibits no photobleaching, a long luminescence lifetime, a large Stokes shift and high quantum efficiency. Fourth, the sensor preferably is capable of monitoring physically remote locations and may preferably be miniaturized into a small flexible probe.
Improvements in sensor technologies are always sought in order to improve the various chemical and biological processes, such as those identified above, which rely on sensors. An oxygen sensor with the attributes identified above would represent a significant advance in the field.